Abstract
Intradermal tumors derived from three rat neurogenic tumor cell lines were treated by magnetic induction hyperthermia involving a ferromagnetic implant with a low Curie temperature. A single session of hyperthermia (1 hour at 45°C) against the T9 tumor was apparently effective: almost all of the tumors disappeared. However, hyperthermia had no obvious effects on the other two tumors, even after repeated treatments at weekly intervals. Histological study of T9 intradermal tumors following hyperthermia showed marked loss of cells and diffuse edema as well as venous dilatation and bleeding by day 0, granulocytic infiltration by day 4, and massive lymphocytic infiltration by day 8. On the 14th day extensive necrosis and lymphocytic infiltration were observed within the tumor. At this point most of the tumors had shrunk considerably. Cultured T9 tumor cells subjected to water bath hyperthermia for 1 hour at 46°C and then injected intradermally into rats failed to develop into tumors. Weekly injections of such T9 cells produced no recognizable immunity in the rats, as proven by the growth of tumors in subsequent challenges with untreated T9 tumor cells. However, treating the T9 tumor cells by hyperthermia for 1 hour at 42°C before injection produced apparent immunity in the rats, although one half of the immunizing injections resulted in the development of small intradermal tumors.
The results indicate an immunogenic activity in heat-treated tumor cells. The involvement of immunological factors in the regression of intradermal neurogenic tumors following hyperthermia was demonstrated.
